1. Field of the Invention
The present invention generally relates to internal combustion engines and, more particularly, toward cooling flow structures and methods in a cylinder block of multi-cylinder internal combustion engines.
2. Description of Related Art
Siamese-type engine blocks minimize the length and weight of the engine by eliminating the space between adjacent cylinders and, as such, include cylinders having conjoined walls. Multi-cylinder siamese-type internal combustion engines are typically cooled by circulating coolant through a water jacket formed between the cylinder walls and the engine block.
A conventional engine block cooling arrangement is schematically illustrated in FIG. 14, wherein the siamese-type cylinder walls 110, the water jacket 111 and the head 112 are schematically illustrated. In this arrangement, coolant is introduced into the water jacket 111 via an inlet 114, and flows around both sides of the cylinders 110. A head gasket 113 is disposed between the upper surface of the engine block and the head 112, and coolant flows upwardly through holes 116 formed in the head gasket 113 into the head 112. It is noted that a major portion of the gasket holes 116 are formed in an end of the head gasket 113 opposite the coolant inlet 114. As such, a relatively major portion of coolant flows from the inlet end of the water jacket 111 to the opposite end of the water jacket and through the major portion of the gasket holes 116, and a relatively minor portion of the coolant flow goes through the head 112, perhaps only 30% of the total flow.
Unfortunately, due to the structure of such cylinder blocks and the flow of combustion gases, temperature differences exist between different sides of the cylinders (i.e., intake v. exhaust), different ends of the cylinders (top v. bottom) and between different cylinders (i.e., end cylinders v. internal cylinders). These temperature differences are not addressed in the aforementioned conventional cooling arrangement, and create problems in maintaining generally consistent cylinder temperatures.
For example, the heat path to coolant flow from the siamese regions (i.e., conjoined regions of adjacent cylinders) is longer than the heat path to coolant flow from other areas, and inevitably results in non-uniform temperature distribution on the combustion chamber surface. This, in turn, causes thermal expansion differences between inner, conjoined portions of the cylinder walls, which lack direct contact with a cooling water passage, and external portions of the cylinder walls, which are in direct contact with a cooling water passage. Thus, it is desirable to improve the cooling efficiency at the conjoined portions as compared to the non-conjoined regions so as to reduce this temperature difference.
Also, along the circumference of a cylinder, the exhaust-side cylinder wall surface is hotter than the intake-side cylinder wall surface. Thus, it is desirable to improve the exhaust-side cylinder wall cooling efficiency relative to the intake-side cylinder wall cooling efficiency so as to reduce a temperature difference or gradient between the exhaust side of the cylinder and the intake side of the cylinder.
Further, the cylinder walls, when viewed in an axial direction, also require different cooling capabilities because the upper portion of the cylinder is exposed to hotter combustion gas than the lower portions of the cylinder, and, furthermore, because the upper portion surface is exposed to combustion gas longer than the lower portion. Accordingly, it is desirable to improve cooling efficiency at the cylinder upper portions as compared to the cylinder lower portions so as to reduce these temperature differences.
When viewed in total, it is generally desirable to have higher cooling capacities on the exhaust side and upper end of the cylinders as compared to the intake side and lower end of the cylinders.
Temperature differences in the cylinder wall may result in engine operational problems. For example, if the cylinder wall is distorted due to differing amounts of thermal expansion, the piston ring at the upper side of the piston, which reciprocates vertically within the cylinder, does not uniformly seal to the cylinder wall but rather will partially stick to the cylinder wall at some locations and loosely slide over the cylinder wall at other locations. Temperature uniformity along the cylinder axis improves clearance or clearance tolerance between the piston and cylinder wall surface as the piston reciprocates within the cylinder bore, and therefore reduces friction and improves sealing throughout the piston stroke. Accordingly, a uniform temperature in the circumferential and axial directions is desired so as to permit uniform sealing engagement between the piston ring and the cylinder wall, while having minimal frictional resistance during reciprocating movement of the piston. Moreover, it is desirable to arrange the cooling flow in multi-cylinder engines such that temperature distribution on each cylinder wall is as close as possible to reduce cylinder-to-cylinder variation of power output.
In addition to the problems associated with thermal deformation, an auto-ignition tendency in spark ignition engines is related to combustion chamber surface temperature. Reducing hot spot temperature (i.e., localized areas of increased temperature) reduces the chances for auto-ignition, and has a positive impact on engine performance and fuel economy.
It is also known that the sooner an engine reaches ideal operating temperature conditions, the more efficiently it operates. Therefore, it is desirable to reduce the heat removal rate on the lower portion of the cylinder walls to accelerate warming-up of engine oil through crankcase walls, to accelerate warming-up of the cylinder walls, and to improve engine fuel economy by reducing heat loss.
Much work has been done in the past in response to these needs. For example, U.S. Pat. No. 5,558,048 discloses an engine cooling system that reduces cylinder wall deformation. For an engine having a plurality of cylinders that are arranged along a longitudinal axis of the engine, an intermediate wall is provided between every two adjacent bores. The '048 patent teaches forming a cutout in the siamese areas to improve cooling.
U.S. Pat. No. 5,542,381 attempts to improve cooling flow rate and heat transmission in the Siamese areas by including flow guide ribs in a central position inside the passage with respect to the vertical width of the passage. However, the '381 patent discloses improving cooling in the hollow areas, while it is known that the upper regions of the cylinder are under much higher thermal loading than the lower regions of the cylinder. Furthermore, efficient installation of such guide ribs during mass production presents a major obstacle.
Thomas Heater et al. (U.S. Pat. No. 5,253,615) proposes to shorten engine warm-up with shallow water jackets surrounding its cylinders. In order to maintain uniform wall thickness and prevent combustion noise from emitting directly to the outside, an isolation chamber is formed in the area between the shallow water jacket and the top of the crankcase cavity. However, this design significantly complicates high-pressure aluminum die casting, which is widely used to manufacture cylinder blocks.
Tokkai Hei 4-136461 published by the Japanese Patent Office in 1992 proposes decreasing the width of the water jacket midway along its height so as to increase the flow velocity of cooling liquid through the siamese areas.
Masato Kawauchi et al. (U.S. Pat. No. 5,207,189) attempts to eliminate coolant flow stagnation by forming a plurality of annular passages between a cylinder block and the cylinder liner fitted in the cylinder block, especially for wet-liner engine block.
Jocken Betsch et al. (U.S. Pat. No. 5,988,120) utilizes a displacement body in the coolant space to reduce effective coolant space volume. Therefore, an intensive cooling is achieved with a reduced coolant quantity for the entire bore surface.
Habuo Nobu (U.S. Pat. No. 4,569,313) attempts to improve cooling uniformity of engine cylinder head and block by implementing block partition walls between cylinders.
David Boggs (U.S. Pat. No. 5,746,161) proposes a tapered water jacket along the cylinder axis to improve the uniformity of cylinder wall temperature. Unfortunately, the passage thickness at the bottom is limited by the manufacturability, or imposes significant cost increases, and therefore the Boggs structure has proven to be commercially or functionally impractical.
Sassan Etemad (U.S. Pat. No. 6,138,619) suggests a flow directing device protruding from a support element above the top surface of a block to improve cooling. However, the proposed method is expensive and has a negative impact on combustion gas sealing. Furthermore, it does not affect temperature uniformity and shortening of engine warm-up.
Yoshikazu Shinpo and Takashi Matsutani (US Patent Application Publication No. 2002/0000210) attempt to achieve uniform cylinder wall temperature by disposing a spacer in the water jacket. The ideas as described in embodiments 1 to 10 will increase cylinder wall temperature of lower portion, which will adversely affect piston heat dissipation capability and engine performance due to charge heating. Embodiments 45 to 48 address high cylinder wall temperature problems at high engine speed, but require devices to adjust flow rate, which increases the cost and requires a new engine block design and a new coolant flow layout.
Accordingly, while various attempts have been made to address one or more of these competing concerns, there remains a need in the art for a method and device that reduces temperature variation within each cylinder and between adjacent cylinders in a multi-cylinder siamese-type internal combustion engine.